2-Amino-s-triazines are important products having important utilities as plant protection agents, optical brighteners and as pharmaceutical agents. Synthesis methods starting from cyanuric chloride are known for most of these compounds. However, if s-triazine derivatives with alkyl substituents in the 4- or 6-position are to be prepared, starting substances other than cyanuric chloride must be used.
Thus, the preparation of 2-amino-4-alkyl-6-methoxy (ethoxy)-s-triazines is known from French Pat. No. 1,380,818, the corresponding triazines being formed by a cyclization reaction of guanyl-O-methyl (or ethyl)-isourea with carboxylic acid chlorides or carboxylic acid esters. However, this method is only suitable on a laboratory scale, since the yields are extremely low and the guanyl-O-methyl- and guanyl-O-ethyl-isourea hydrochloride required as starting substances are only accessible with difficulty and are thus unavailable on an industrial scale.
According to U.S. Pat. No. 3,754,547, 2-amino-s-triazine derivatives can be prepared by reaction of N-cyanimido-esters with guanidine, O-methylisourea or amides. This process is also unsuitable on an industrial scale, since the yields produced are only about one-half of the desired yield (a maximum yield of 45% results in the case of the important compound 2-amino-4-methoxy-6-methyl-s-triazine), and the free O-methylisourea base, which is relatively unstable, must be used as the starting substance in this process.
Another preparation route, for example, for 2-amino-4-methoxy-6-methyl-s-triazine, involves the reaction of N-cyanoacetimido-esters with sodium hydrogen cyanamide in methanolic solution, sodium N, N-dicyanoacetamidine being formed as the intermediate (cf. K. R. Huffmann and F. C. Schaefer, J. Org. Chem. 28, page 1816 (1963)). The desired product is then formed in 65% yield by cyclizing the intermediate in the presence of methanol and excess hydrogen chloride. This process is also relatively complicated and therefore too difficult and too expensive for use as an industrial process.
N-Cyanimido-esters of the general formula I are also important synthesis units for the preparation of plant protection agents, pharmaceuticals and other fine and specialized chemicals: ##STR1## R.sub.1 =H, alkyl with 1 to 24 carbon atoms, aralkyl or aryl; R.sub.2 =alkyl with 1 to 4 carbon atoms.
Although a two-stage process for the preparation of N-cyanimido-esters has been known for a long time, such process was suitable only for use on a laboratory scale. In the first stage, to prepare the imido-ester hydrochlorides, hydrogen chloride was usually passed into a equimolar mixture of alcohol and nitrile and the mixture was left to stand for a prolonged period, the reaction mixture solidifying as the reaction progressed (cf. A. Pinner "Die Imidoather and ihre Derivate" ("The imido-ethers and their derivatives") Berlin 1892). This reaction is difficult to carry out in industry as in the use of diethyl ether and dioxane as diluents. According to U.S. Pat. No. 3,402,193, the preparation of butyramidine hydrochloride is described, using an excess of butyronitrile. However, the butyrimido-ethyl ester hydrochloride which is probably formed as an intermediate is not isolated and identified. In the preparation of butyramidine hydrochloride in the presence of butyl acetate, according to U.S. Pat. No. 3,538,139, there is also no isolation and identification of the butyrimido-ethyl ester hydrochloride which is probably formed as an intermediate. The yield of butyramidine hydrochloride is only 33%, and 45% of the unreacted butyronitrile is recovered. None of these known processes for the preparation of imido-ester hydrochlorides can be used industrially, either because the yields are too low or because of the cumbersome preparation methods.
Also, for the second stage, i.e., the preparation of N-cyanimido-esters from the imido-ester hydrochlorides and cyanamide, no processes are known which appear to be industrially useful both with respect to the yields and with respect to the byproducts obtained. Thus, for example, according to U.S. Pat. No. 3,225,077, the preparation of N-cyanimido-esters by the action of solid, anhydrous cyanamide on the corresponding acetimido-ester hydrochloride in alcoholic solution is described. Aside from the relatively low yields of not more than 66%, this synthesis route is relatively expensive and thus uneconomical, because solid, anhydrous cyanamide must be used as the starting substance.
The preparation of N-cyanoacetimido-ethyl ester hydrochloride in aqueous solution is therefore a preparative advance (cf. W. Lwowski, Synthesis 1971, page 263), the reaction being carried out in the presence of stoichiometric amounts of disodium hydrogen phosphate. The decisive disadvantages of this procedure are the low yield of 58%, based on the acetimido-ester hydrochloride, the release of ammonia and the formation of sodium chloride and sodium dihydrogen phosphate as byproducts.